Since the days of Jim Crow, a fairly unified white Southern vote has often determined the outcome of elections.

This November could be different. Nearly five decades after the passage of the Voting Rights Act, black voters in the South are poised to play a pivotal role in this year’s midterm elections. If Democrats win the South and hold the Senate, they will do so because of Southern black voters. […]

This year’s closest contests include North Carolina, Louisiana, and Georgia. Black voters will most likely represent more than half of all Democratic voters in Louisiana and Georgia, and nearly half in North Carolina. Arkansas, another state with a large black population, is also among the competitive states. […]

If Democrats win this November, black voters will probably represent a larger share of the winning party’s supporters in important states than at any time since Reconstruction.

Meanwhile, the reliance of southern Democratic candidates on black voters is partly a product of a generational shift which is leaving behind a period during which southern Dems didn’t depend on them at all — but now turnout is high enough among southern blacks to change that:

Today, the overwhelming majority of voters, white and black alike, reached voting age after the passage of the Voting Rights Act. Southern politics are now defined by the post-Civil Rights era: The old generation of Southern white Democrats has almost entirely departed the electorate, leaving white voters overwhelmingly Republican. Mr. Obama won about 15 percent of white voters in the Deep South in 2012.

Democrats lamented low black turnout for decades, but Southern black turnout today rivals or occasionally exceeds that of white voters. That’s in part because black voters, for the first time, have largely been eligible to vote since they turned 18. They have therefore had as many opportunities as their white counterparts to be targeted by campaigns, mobilized by interest groups or motivated by political causes.

There’s an additional historical irony here worth savoring. Nearly 50 years after the Voting Rights Act, the current battle over voting rights — the Republican drive to restrict “voter fraud,” and the Democratic counter-argument that it’s really about disenfranchising Democratic voter groups, particularly minorities — could play a key role in determining whether southern blacks turn out in the numbers needed to save Democratic control of the Senate.

In North Carolina, SCOTUS’ decision undermining the Voting Rights Act was followed by the passage in the state legislature — presided over by the GOP Senate candidate, state House speaker Thom Tillis — a law restricting early voting and eliminates same-day voting, and requires Voter ID. Critics argue the measure disenfranchises blacks, and invoking it will be key to Dem efforts to mobilize African American turnout this fall. The state NAACP is already citing the new law to mobilize voter registration. Meanwhile, a federal judge may end up putting the law itself on hold until after the election — which won’t stop Dems from using it to mobilize voters.

In Arkansas, Democratic Senator Mark Pryor’s campaign has already been invoking the state’s recent voter ID law — passed by a GOP-controlled legislature — to mobilize African Americans. That law was recently struck down by a judge but remains in effect, and Arkansas Dems will counter by invoking it in efforts to mobilize black voters this fall.

In Louisiana the state Democratic Party has a full time staffer devoted to outreach in the black and faith-based communities that is all about adding voters to the rolls. The Dems’ message regularly emphasizes the history of civil rights in the region — as well as Republican voter policies and GOP invocations of “voter fraud” — to urge blacks to exercise the franchise, and you can expect that to be part of mobilizing efforts heading into Election Day. Black turnout could be critical to control of the Senate if it all comes down to a runoff in Louisiana (in 2002 Dem Mary Landrieu showed she can drive out large numbers of African Americans in off-year midterm runoffs).

The unknown is whether these laws will depress African American turnout — particularly in North Carolina and Arkansas — or whether Dem invocations of those laws could end up driving more voters out than otherwise might have voted in what should be a bad turnout year for Dems. We already saw an odd outcome in Mississippi, where unexpected numbers of African Americans turned out for a Republican (Thad Cochran) after his Tea Party opponent called on poll-watchers to be vigilant for just that possibility.

Could southern blacks save the Senate for Dems? Could the GOP drive to restrict voting backfire and help it happen? Politics and history can be strange and unpredictable.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.

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